linux-kernel - Re: Updating cypress/brcm firmware in linux-firmware for CVE-2019-15126

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Date:   Thu, 05 Mar 2020 11:16:46 +0200
From:   David Woodhouse <dwmw2@...radead.org>
To:     Hans de Goede <hdegoede@...hat.com>, chi-hsien.lin@...ress.com,
        Christopher Rumpf <Christopher.Rumpf@...ress.com>,
        Chung-Hsien Hsu <cnhu@...ress.com>
Cc:     linux-firmware@...nel.org,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: Updating cypress/brcm firmware in linux-firmware for
 CVE-2019-15126

On Thu, 2020-03-05 at 07:24 +0100, Hans de Goede wrote:
> > also clm_blob download is not supported in kernels prior to 4.15 so
> > those files won't work with older kernels.
> 
> That is a valid concern, I'm not sure what the rules for linux-firmware
> are with regards to this.

Not quite sure I understand the problem.

The rules for Linux firmware are just the same as basic engineering
practice for loadable libraries.

If you change the ABI, you change the "soname" of a library, which
equates to changing the filename of a linux-firmware object.

So if you make a new file format for the firmware which requires new
driver support, then you give it a new name. The updated driver can
attempt to load the old firmware filename as a fallback, if it still
supports that, or you just have a clean separation between the two.

The linux-firmware repository then carries *both* files, supporting
both old and new kernels in parallel.

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